Diffusion curve

Diffusion curves are vector graphic primitives for creating smooth-shaded images. Each diffusion curve partitions the 2D graphics space through which it is drawn, defining different colors on either side. When rendered, these colors then spread into the regions on either side of the curve in a way analogous to diffusion. The colors may also be defined to vary smoothly along the curve and the sharpness of the color transition from one side of the curve to the other may also be specified.

Original PhD thesis introducing concept of Diffusion curves.

Diffusion curves have been discussed in relation to being a possible addition to the SVG specification.

Motivations

In the original paper introducing the concept of diffusion curves, Orzan et al. describe two main motivations for them.

Freehand drawing

Artists traditionally begin by sketching lines and shapes that represent the major, and some of the lesser, colour boundaries of the envisioned work. The use of diffusion curves supports this practice accurately: as color would be added later, up to and between these sketched lines, so the lines' color values are specified and their 'diffusion-like' behaviors produce an image in a manner similar to the way a traditional artist works with brushes or other media.